Light emitting device with self-aligning preformed lens

ABSTRACT

A light emitting diode (LED) light source is disclosed. The LED light source comprises a lens structure that includes a hemispherical dome with a base. The LED light source comprises a cavity in the base. The cavity has an opening and a taper such that a cross-section area within the cavity is smaller than an area of the opening. The LED light source comprises a light emitting device comprising an LED die contacting the taper. The taper allows for easy insertion of the LED die into the lens structure. The taper serves to accurately align the LED die when the LED die is inserted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/110,840 filed on Jul. 11, 2016, which is the U.S. National Stage,under 35 U.S.C. § 371 of International Application No.PCT/IB2015/050050, filed Jan. 4, 2015, which claim priority to U.S.Provisional Application No. 61/930,586 filed Jan. 23, 2014.

FIELD OF THE INVENTION

This invention relates to the field of light emitting devices, and inparticular to a light emitting device that is formed by placing a selfsupporting light emitting element into a preformed lens having a cavitywith sloped walls that facilitate insertion of the light emittingelement into the lens and facilitate adhering the light emitting elementto the lens.

BACKGROUND OF THE INVENTION

Conventional light emitting devices include a light emitting element,such as a light emitting diode chip (LED chip) mounted on a substrateand encased in a protective enclosure that may serve as an optical lens.The substrate provides the structural support required to facilitatehandling of the light emitting device during subsequent processes, suchas the mounting of the light emitting device on a printed circuit board.The protective enclosure may include a wavelength conversion materialthat converts at least a part of the light emitted from the lightemitting chip to light of a different wavelength. The wavelengthconversion material may alternatively be provided as a discrete elementbetween the light emitting chip and the enclosure/lens.

Common techniques for providing a light emitting device as describedabove include attaching the light emitting element to a wire framesubstrate that serves to allow external power connections to the lightemitting element, then encapsulating the light emitting element and theportion of the wire frame to which it is attached with a silicone mold.The wire frame may be part of a carrier that includes multiple framesfor mounting light emitting elements, such that the encapsulation can beperformed for all of the light emitting elements as a single moldingprocess.

In another embodiment, the light emitting element is mounted on aceramic substrate that includes conductors to which the light emittingelement is attached. U.S. Pat. No. 7,452,737, “MOLDED LENS OVER LEDDIE”, issued 18 Nov. 2008 to Grigoriy Basin, Robert Scott West, and PaulS. Martin, discloses a ceramic substrate that accommodates multiplelight emitting elements, and a mold that forms a lens element over eachof the light emitting elements. The ceramic substrate may subsequentlybe sliced/diced to provide‘singulated’ light emitting devices thatinclude external connections to the light emitting element on theceramic substrate.

In another embodiment, the substrate includes cup-like cavities withinwhich the light emitting elements are attached to conductors forcoupling the light emitting element to a power source. The lightemitting elements are encapsulated by filling the cavities with a lowviscosity silicone and curing the silicone. The cavity may be shaped toprovide a particular optical effect, and/or a mold may be used to form adesired lens structure above the cup. U.S. Pat. No. 7,214,116,“LIGHT-EMITTING DIODE AND METHOD FOR ITS PRODUCTION”, issued 8 May 2007to Akira Takekuma, discloses placing a preformed lens atop the siliconewithin the cup. After curing the silicone, the substrate is diced toprovide the singulated light emitting devices.

Each of the above processes requires singulating the light emittingdies, mounting each die on the substrate, encapsulating the dies on thesubstrate, then slicing/dicing the substrate to singulate the completedlight emitting devices. In addition to the additional manufacturing costand effort associated with the double-handling involved with theintermediate step of mounting the light emitting dies on a substrate,this double-handling process also challenges applications wherein thelight emitting die is required to have a particular location withrespect to the optics of the enclosing structure. In many applications,if the light emitting element is ‘off-center’ relative to the optics ofthe enclosing structure, the formed light emitting device may bediscarded as ‘failed’ in the manufacturing process, or may pass themanufacturing test and result in a defective product when it isincorporated into the product. For example, in a camera-flashapplication, if the camera/cell-phone/tablet/etc. produces pictures withnon-uniform illumination, the purchaser of thecamera/cell-phone/tablet/etc. will likely demand a replacement.

Although fairly simple techniques are available to properly align thesubstrate with the tool that provides the molded lens structure, such ascreating alignment features in each of the substrate and the tool,achieving a correspondingly proper alignment of the light emittingelement on the substrate is a more challenging and costly task,requiring, for example, a high-precision ‘pick-and-place’ machine toplace each light emitting element at a highly-precise location on thesubstrate.

In order to avoid the aforementioned double-handling of the lightemitting element, technologies have evolved to provide light emittingdies that are self-supporting, and can be handled directly. WO2013/084155, “FORMING THICK METAL LAYERS ON A SEMICONDUCTOR LIGHTEMITTING DEVICE”, published 13 Jun. 2013 for Schiaffion, Akram, Basin,Munkhol, Lei, and Nickel, and incorporated by reference herein,discloses light emitting elements that have thick metal layers thatprovide the structural support required for routine handling of theelements, eliminating the need for a supporting substrate. Because theself-supporting chip can be handled without further packaging, it iscommonly termed a “Chip Scale Package” (CSP).

However, even though these self-supporting chips do not require astructural substrate, the conventional encapsulation processes stillrequire that these chips be placed on some form of substrate, to allowmultiple chips to be encapsulated at the same time, with theaccompanying difficulty in assuring alignment of the light emitting chipand the attached lens structure.

SUMMARY OF THE INVENTION

It would be advantageous to provide a method and system that facilitatesaccurate alignment of light emitting chips and their associated lensstructures. It would also be advantageous if this method and system aresuitable for mass production processes.

To better address one or more of these concerns, in an embodiment ofthis invention, a lens structure is pre-formed with features thatfacilitate accurate alignment of a light emitting chip within the lensstructure. To ease manufacturing, the features include tapered wallsthat allow for easy insertion of the light emitting chip into the lensstructure, the taper serving to accurately align the light emitting chipwhen the chip is fully inserted. The taper may include linearly slopedor curved walls, including complex shapes. An adhesive may be used tosecure the light emitting chip to the lens structure. The light emittingchips may be ‘picked and placed’ into an array of lens structures, or‘picked and placed’ onto a substrate that may be overlayed by the arrayof lens structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail, and by way of example,with reference to the accompanying drawings wherein:

FIGS. 1A-1B illustrate an example profile and bottom view of a lensstructure with sloped walls and channels that facilitate the exit of airbubbles and adhesives.

FIG. 2 illustrates an example profile view of a lens structure withstepped and sloped walls.

FIGS. 3A and 3B illustrate example sheets of lens structures withtapered cavities.

FIGS. 4A-4D illustrate example profiles of complex tapered cavities.

FIG. 5 illustrates an example bottom view of a lens structure with aconic-section cavity.

FIGS. 6A and 6B illustrate alternative optical elements.

Throughout the drawings, the same reference numerals indicate similar orcorresponding features or functions. The drawings are included forillustrative purposes and are not intended to limit the scope of theinvention.

DETAILED DESCRIPTION

In the following description, for purposes of explanation rather thanlimitation, specific details are set forth such as the particulararchitecture, interfaces, techniques, etc., in order to provide athorough understanding of the concepts of the invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced in other embodiments, which depart from these specificdetails. In like manner, the text of this description is directed to theexample embodiments as illustrated in the Figures, and is not intendedto limit the claimed invention beyond the limits expressly included inthe claims. For purposes of simplicity and clarity, detaileddescriptions of well-known devices, circuits, and methods are omitted soas not to obscure the description of the present invention withunnecessary detail.

FIGS. 1A-1B illustrate an example profile and bottom view of a lens 100that includes a cavity 150 for receiving a light emitting device (LED)110, and an optical element 140 that provides a desired light outputpattern when light is emitted from the LED 110. In this example, theoptical element 140 is a hemispherical dome that provides asubstantially uniform light output pattern across its field of view.

The lens 100 may comprise silicone, a silicone epoxy hybrid, glass, orany transparent optical material with an appropriate refractive index.The LED 110 may be a self-supporting device, such as achip-scale-package (CSP), or a thin film die mounted on a ceramicsubstrate (die on ceramic, DOC), with contacts 120 on the surfaceopposite the light emitting surface 130. Other LED structures may alsobe used.

As illustrated, to ease assembly, the cavity 150 is tapered, andincludes sloped walls 160. The bottom surface 170 of the cavity 150 isdimensioned so as to situate the light emitting device 110 at a fixedlocation within the cavity 150 within a given precision, based on therequirements of the intended application. In this example, the bottomsurface 170 has substantially the same dimensions as the light emittingdevice, although it may be slightly larger, depending upon thetolerances of the light emitting device. The required precision of thelocation of the light emitting device 110 with respect to the lensstructure 100 may dictate the allowable over-sizing, if any, of thebottom surface 170.

An adhesive having a refractive index that is equal to the refractiveindex of the LED 110 or the lens 100, or a value between the refractiveindexes of the LED 110 and lens 100 may be dispensed into the cavity 150before the LED 110 is inserted into the cavity. Depending upon theparticular assembly technique, the adhesive may also, or alternatively,be dispensed upon the LED 110 prior to insertion into the cavity 150.

As illustrated in FIGS. 1A and 1B, channels 180 may be provided toenable air and excess adhesive to escape during the assembly process.These channels 180 are illustrated as cylindrical borings in FIGS. 1Aand 1B, although other shapes may be used; for example, if the cavity isformed by a molding process, the channels may have the same slope as thesloped walls 160.

The channels 180 are illustrated at each corner of the cavity 150,although other locations, and fewer or more channels may be provided. Inone alternative channels located at the sides of the LED 100 and awayfrom the corners may be used to avoid rotational alignment errors. Thesize, shape, and location of the channels may be altered depending uponmultiple factors including, for example, the viscosity of the adhesive,and the overall size of the LED 110.

In another embodiment, the LED 110 is inserted into the cavity withoutan adhesive between the light emitting surface 130 and the bottomsurface 170 of the cavity 150. A thin film of index-matched liquid maybe used to provide an efficient optical coupling between the LED 110 andthe bottom surface 170. After insertion, an adhesive may be administeredin the space between the LED 110 and the sloped walls 160. Thispost-insertion application of the adhesive may eliminate or minimize theneed for the channels 180.

To ease subsequent mounting of the lens 100 with LED 110 on a subsequentsubstrate, such as a printed circuit board, the depth of the cavity 150may be determined such that the contacts 120 extend slightly above(‘proud of) the underside 101 of the lens 100 when the light emittingdevice is fully situated within the cavity. A depth that is about 50-500um less than the total height of the LED 110, including contacts 120,generally provides a sufficient pride0 of the contacts beyond theunderside 101 of the lens 100, although other depths may be used,depending upon the tolerance requirements of the application. Forexample, if the LED 110 is a self-supporting chip-scale package, withfine tolerances, a nominal proud as small as 5 um may be used.

By shaping the taper such that the opening of the cavity 150 is largerthan the dimensions of the LED 110, insertion of the LED 110 into thecavity 150 is simplified. By shaping the taper such that thecross-section of the cavity 150 narrows in a direction toward the bottomsurface 170, variance in the location of the LED 110 within the lens 100is substantially controlled, providing for a self-alignment of the LED110 as it is inserted into the lens 100. This taper also provides thisself-alignment independent of the means used to insert the LED 110 intothe cavity 150. Even a manual insertion of the LED 110 into the cavity150 will provide the same accuracy and precision as an automatedinsertion using a highly accurate and precise pick-and-place machine. Inlike manner, a pick-and-place machine of minimal accuracy and precisionmay be used while still maintaining the same high level accuracy andprecision.

As illustrated in FIG. 2, the profile of the cavity 250 of lens 200 maybe adjusted to conform to the shape of the light emitting device 210. Inthis example, the light emitting device 210 includes a wavelengthconversion layer 230, such as a phosphor-embedded silicone that ismolded upon the light emitting device 210. A recess 265 at the entry tothe cavity 250 is shaped to accommodate the lip 235 formed by thisexample wavelength conversion layer 230.

Below the recess 265, the cavity 250 includes sloped walls 260 tofacilitate insertion of the light emitting device 210, and a bottomsurface 270 that serves to locate the light emitting device within thelens 200 within a given precision, as detailed above with regard tosurface 170 of lens 100.

FIGS. 3A and 3B illustrate example sheets 300, 300′ of lenses 100, 100′with cavities 150. Although only a few lenses 100, 100′ are illustrated,one of skill in the art will recognize that the sheets 300, 300′ mayinclude hundreds of lenses 100, 100′. For ease of illustration, theventing channels 180 of each cavity 150 of FIGS. 1A-1B are notillustrated, but may be present.

In the example of FIG. 3A, sheet 300 includes sixteen lenses 100, eachwith a single cavity 150. This sheet may comprise, for example silicone,a silicone epoxy hybrid, glass, or any other transparent opticalmaterial that can be formed with defined cavities.

In an example manufacturing process, a pick and place machine may beused to insert each LED 110 (not illustrated) into each cavity 150. Thepick and place machine may be configured to place each LED 110 at thecenter of each cavity 150, but with sufficient compliance during theinsertion to enable the LED 110 to be guided by the walls of the cavity150 into the desired location. Alternatively, the pick and place machinemay place each LED 110 partially into each cavity 150, and a subsequentprocess, such as a plate press may be used to complete the insertion ofthe LEDs 110 into the cavities 150.

In an alternative process, the LEDs are arranged on a temporarysubstrate, such as a conventional “dicing tape”, at appropriatelocations, and the sheet 300 is mated with these LEDs on the substrate,by either overlaying the sheet 300 upon the LEDs, or overlaying thedicing tape with attached LEDs over the sheet 300.

In an example embodiment, the sheet 300 is a partially cured siliconethat is cured after the LED 110 is inserted into each cavity 150. Thesubsequent curing may serve to adhere each LED 110 to each lens 100,thereby avoiding the need to include an adhesive bond.

In an alternative embodiment, the sheet 300 is fully formed, and anadhesive may be applied to each cavity 150, or to each LED 110, tosecure each LED 110 to each lens 100. In some embodiments, the adhesiveis applied after the LEDs 110 are inserted into the cavities 150,adhering the edges of the LEDs 110 to the walls of the cavities 150.

In other embodiments, detailed below, the sheet 300 may comprise amaterial with some resilience, and the insertion of the LED 110 into thecavity 150 may provide a sufficient friction force to maintain the LED110 at the appropriate location within the lens 100.

A material that facilitates optical coupling between the light emittingsurfaces of the LEDs 110 and the lenses 100 of the sheet 300 may beapplied to either the cavities 150 or the LEDs 110.

In like manner, a material that serves to reflect light that strikes theedges of the LED 110 may be applied to the edges of the LED 110, forexample, by filling the gap between the LED 110 and the sloped walls ofthe cavity 150 with such material.

Upon completion of the insertion and adhering of the LEDs 110 in theCavities 150 of the lenses 100, the sheet 300 may be sliced/diced alongthe cutting lines 320-370 to provide singulated LED with lensassemblies. In some embodiments multiple LED with lenses may be providedas a single assembly, for example, by only slicing along lines 330 and360, providing four assemblies, each assembling including four LEDs withindividual lenses.

One of skill in the art will recognize that the example one-to-onerelationship between LEDs and lenses of the previous figures is merelyone of many configurations. For example, FIG. 3B illustrates anembodiment wherein multiple LEDs are intended to be inserted intomultiple cavities 150 of each lens 100′. In such an embodiment, thecavities 150 of each lens 100′ may be more closely situated than thecavities 150 of each lens 100 of FIG. 3A.

In some embodiments, one or more of the cavities 150 may be configuredto accommodate multiple LED dies, which may be arranged on a singlesubstrate. In other embodiments, the cavities 150 within each lens 100′may be of different sizes, to accommodate a mix of different LED typeswithin the lens 100′, such as a combination of different color LEDs.

As in the example of FIG. 3A, the LEDs 110 (not illustrated) may beinserted into each cavity manually, or via a pick-and-place process. Or,the LEDs 110 may be arranged on a temporary substrate at locationscorresponding to cavities 150 on the sheet 300′, and subsequently matingthe sheet 300′ and the substrate containing the LEDs 110. Similarly, theLEDs 110 may be adhered to the lenses 100′ using any of the abovedescribed techniques, or any other viable and reliable technique.

Upon completion of the insertion and adhering of the LEDs 110 into theCavities 150 of each lens 100′, the lenses 100′ may be singulated byslicing/dicing the sheet 300′ along the cutting lines 380, 390.

One of skill in the art will recognize, in view of this disclosure, thatthis invention is not limited to the example use of cavities 150 withlinearly sloped walls 160.

FIGS. 4A-4D illustrate alternative cavity profiles. As in FIGS. 3A-3B,the venting channels 180 of FIG. 1 are not illustrated in these figures,for ease of illustration, but may be included in each exampleembodiment.

FIG. 4A illustrates a profile comprising wall segments 410, 420 havingdifferent slopes. The upper wall segment 410 has a relatively shallowslope to provide a wide opening for inserting the LED (not illustrated),while the wall segment 420 has a relatively steep slope, and may beorthogonal to the surface 470, to provide a larger surface area forconstricting the edges of the LED to maintain the proper location of theLED within the cavity.

Depending upon the material in which the cavity is formed, the closenessof the fit between the size of the LED and the size of the surface 470,the slope of the lower wall segment 420, and the size of the ventingchannels 180 (not illustrated), this embodiment may require substantialforce to insert each LED into each cavity. FIGS. 4B-4D illustratealternative profiles that may require less insertion force.

In FIG. 4B, the upper wall segment 430 is sloped to provide an openingthat is larger than the size of the intended LED, and the lower wallsegment 420 is sloped in an opposite direction to create protrusions 435that serve to constrict the edges of the LED to maintain the properlocation of the LED within the cavity. However, as compared to FIG. 4A,the edges of the LED will only contact these protrusions 435, and notthe entire surface of the lower wall segment 440. The reversed slope ofthe wall segment 440 provides a lower surface 470 that is wider than theLED that is containing between the protrusions 435, providing some roomfor the displaced air or adhesive, reducing or eliminating the relianceon the venting channels 180.

In FIG. 4C, a curved wall segment 450 is used to gradually reduce thecross section area in the direction of the surface 470 in a non-linearfashion, so that the lower portion of the wall segment 450 may be moreconstraining of the LED compared to the linearly sloped walls 160 ofFIG. 1, but less constraining compared to the linear wall segment 420 ofFIG. 4A, particularly if the segment 420 is orthogonal to the surface470. The continuous curvature of the wall segment 450 may also ease theinsertion of the LED, compared to the abrupt edges at the transitionbetween wall segment 410 and 420 of FIG. 4A.

FIG. 4D illustrates a combination of curved 460 and linear 490 wallsegments, as well as the addition of features 480 that may secure theLED while introducing minimal insertion resistance. The features 480 maybe a continuous ridge within the cavity, or a plurality of individualbead-like protrusions from the wall segment 490. If individualprotrusions are used, the insertion resistance is reduced, and the spacebetween the protrusions allows for the displaced air and adhesive toescape, potentially avoiding the need for the venting channels 180 ofFIG. 1.

One of skill in the art will recognize, in light of this disclosure,that any of a variety of other profiles may be used to fix the locationof the LED within the lens within a given tolerance, while also allowingfor practical insertion forces.

One of skill in the art may also recognize that the shape of the cavity,or the shape of the surface of the cavity, need not match the shape ofthe LED. Depending upon the processes and materials used to create thelens, creating a rectangular cavity, such as illustrated in FIG. B, maynot be economically viable. If, for example, the lens is a rigidmaterial, boring or grinding a circular cavity may be substantially lessexpensive than creating a rectangular cavity.

FIG. 5 illustrates an example lens 500 that includes a conical cavity550 with a sloped wall 560 that forms a circular bottom surface 570. Thediameter of the surface 570 is such that it circumscribes the LED 110,providing contact points 590 on the wall of the cavity that center theLED 110 at the center of the surface 570. The semicircular gaps 575around LED 110 allows for the displaced air and adhesive to escape,potentially avoiding the need for the venting channels 180 of FIG. 1

As contrast to the rectangular surface 170 of FIG. 1B, the conic cavity550 and circular surface 570 may allow the LED 110 to rotate during theinsertion process, but if the optical properties of the lens 500 aresymmetric about the center axis, the rotation of the LED 110 about thiscenter axis will have no effect on the accuracy and precision oflocating the LED 110 at that center axis. If the lens 500 is a partiallycured silicone, the compliance of the partially cured silicone mayenable the LED 100 to “dig in” to the silicone at the corners 590,thereby controlling or limiting the rotation.

It is significant to note that all of the above example profile viewscould also be profile views of half-sections of conic cavities, althoughthe profiles of FIGS. 4B and 4D would more likely be formed by a moldingprocess, rather than a boring or grinding process, and achieving arectangular cavity via a molding process is relatively straightforward.

One of skill in the art will also recognize that the optical element ofthe lens is not limited to the hemispherical dome 140 of FIGS. 1A-1B.FIGS. 6A and 6B illustrate an example side emitting optical element 600,and an example collimating optical element 650, respectively. Otheroptical elements may be used to achieve desired light output patterns.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments.

For example, it is possible to operate the invention in an embodimentwherein additional elements may be included within the cavity. Forexample, a wavelength conversion material may be inserted into thecavity before the light emitting device is inserted. Alternatively, oradditionally, the lens may include a wavelength conversion material, orthe light emitting device may include a wavelength conversion material.In some embodiments, the wavelength conversion material may serve as anadhesive layer between the light emitting device and the lens.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. The mere fact that certain measures are recited inmutually different dependent claims does not indicate that a combinationof these measures cannot be used to advantage. Any reference signs inthe claims should not be construed as limiting the scope.

What is claimed is:
 1. An illumination device, comprising: a lens havinga first surface configured to receive light and substantially direct thelight into the lens, the lens having a second surface, opposite thefirst surface, configured to substantially direct the light out of thelens, the first surface shaped to define a cavity that extends into thelens from a cavity opening to a cavity bottom, the cavity bottom beinggenerally planar, the cavity having an interior bounded by at least onecavity wall that extends between the cavity opening and the cavitybottom, the at least one cavity wall including a first portion thatadjoins the cavity opening, the first portion tapering inward from thecavity opening toward an end of the first portion, the at least onecavity wall further including a second portion that adjoins the end ofthe first portion and tapers outward from the end of the first portiontoward the cavity bottom, such that at the end of the first portion, across-sectional area of the at least one cavity wall, takensubstantially parallel to the cavity bottom, is less than across-sectional area of the cavity opening, taken substantially parallelto the cavity bottom, and less than a cross-sectional area of the cavitybottom, taken substantially parallel to the cavity bottom.
 2. Theillumination device of claim 1, wherein: the first portion tapers inwardmonotonically from the cavity opening to the end of the first portion;and the second portion tapers outward monotonically from the end of thefirst portion to the cavity bottom.
 3. The illumination device of claim1, wherein: a cross-section of the first portion, taken orthogonal tothe cavity bottom, is substantially linear and angled with respect to asurface normal of the cavity bottom; and a cross-section of the secondportion, taken orthogonal to the cavity bottom, is substantially linearand angled with respect to a surface normal of the cavity bottom.
 4. Theillumination device of claim 1, wherein the at least one cavity wallincludes at least one venting channel that is configured to allowdisplacement of material in the cavity.
 5. The illumination device ofclaim 4, wherein the at least one cavity wall includes a plurality ofcavity walls that each extend between the cavity opening and the cavitybottom.
 6. The illumination device of claim 5, wherein the at least oneventing channel includes multiple venting channels that are positionedalong edges between adjacent cavity walls of the plurality of cavitywalls.
 7. The illumination device of claim 5, wherein: each cavity wallincludes a respective first portion that adjoins the cavity opening; therespective first portion tapers inward from the cavity opening toward arespective end of the respective first portion; each cavity wallincludes a respective second portion that adjoins the end of the firstportion and tapers outward from the end of the first portion to thecavity bottom; the ends of the first portions lie substantially in aplane that is substantially parallel to the cavity bottom, such that atthe plane, a cross-sectional area bounded by the cavity walls is lessthan a cross-sectional area of the cavity opening, taken substantiallyparallel to the cavity bottom, and less than a cross-sectional area ofthe cavity bottom, taken substantially parallel to the cavity bottom. 8.An illumination device, comprising: a lens having a first surfaceconfigured to receive light and substantially direct the light into thelens, the lens having a second surface, opposite the first surface,configured to substantially direct the light out of the lens, the firstsurface shaped to define a cavity that extends into the lens from acavity opening to a cavity bottom, the cavity bottom being generallyplanar, the cavity having an interior bounded by at least one cavitywall that extends between the cavity opening and the cavity bottom, theat least one cavity wall including a curved portion that adjoins thecavity opening, the curved portion tapering inward from the cavityopening to the cavity bottom such that the curved portion issubstantially orthogonal to the cavity bottom at the cavity bottom. 9.The illumination device of claim 8, wherein at a location spaced betweenthe cavity opening and the cavity bottom, a cross-sectional area of theat least one cavity wall, taken substantially parallel to the cavitybottom, is less than a cross-sectional area of the cavity opening, takensubstantially parallel to the cavity bottom, and greater than across-sectional area of the cavity bottom, taken substantially parallelto the cavity bottom.
 10. The illumination device of claim 8, whereinthe at least one cavity wall includes at least one venting channel thatis configured to allow displacement of material in the cavity.
 11. Theillumination device of claim 10, wherein the at least one cavity wallincludes a plurality of cavity walls that each extend between the cavityopening and the cavity bottom.
 12. The illumination device of claim 11,wherein the at least one venting channel includes multiple ventingchannels that are positioned along edges between adjacent cavity wallsof the plurality of cavity walls.
 13. The illumination device of claim11, wherein: each cavity wall includes a respective curved portion thatadjoins the cavity opening; the respective curved portion tapers inwardfrom the cavity opening to the cavity bottom, such that at a locationspaced between the cavity opening and the cavity bottom, across-sectional area bounded by the cavity walls is less than across-sectional area of the cavity opening, taken substantially parallelto the cavity bottom, and greater than a cross-sectional area of thecavity bottom, taken substantially parallel to the cavity bottom.
 14. Anillumination device, comprising: a lens having a first surfaceconfigured to receive light and substantially direct the light into thelens, the lens having a second surface, opposite the first surface,configured to substantially direct the light out of the lens, the firstsurface shaped to define a cavity that extends into the lens from acavity opening to a cavity bottom, the cavity having an interior boundedby at least one cavity wall that extends between the cavity opening andthe cavity bottom, the at least one cavity wall including a curvedportion that adjoins the cavity opening and tapers inward from thecavity opening, the at least one cavity wall further including a linearportion that adjoins the cavity bottom and is substantially orthogonalto the cavity bottom, the at least one cavity wall further including afeature disposed between the curved portion and the linear portion, suchthat a cross-sectional area of the feature, taken substantially parallelto the cavity bottom, is less than a cross-sectional area of the cavityopening, taken substantially parallel to the cavity bottom, and lessthan a cross-sectional area of the cavity bottom, taken substantiallyparallel to the cavity bottom.
 15. The illumination device of claim 14,wherein the feature includes a plurality of individual bead-likeprotrusions that protrude from the at least one cavity wall.
 16. Theillumination device of claim 14, wherein the feature includes acontinuous ridge that protrudes from the at least one cavity wall. 17.The illumination device of claim 16, wherein the at least one cavitywall includes at least one venting channel that is configured to allowdisplacement of material in the cavity.
 18. The illumination device ofclaim 17, wherein the at least one cavity wall includes a plurality ofcavity walls that each extend between the cavity opening and the cavitybottom.
 19. The illumination device of claim 18, wherein the at leastone venting channel includes multiple venting channels that arepositioned along edges between adjacent cavity walls of the plurality ofcavity walls.
 20. The illumination device of claim 19, wherein themultiple venting channels are formed as cylindrical borings locatedbetween adjacent linear portions of the cavity walls, each cylindricalboring being substantially orthogonal to the cavity bottom.